|Fer-de-lance pit-viper; infrared sensing pits found below the eyes.|
The specific proteins that the gene code for are receptor proteins. In humans, these receptors, also known as ion channels, drive the response that we have to spicy foods like wasabi. Dr. David Julius and his team found that TRPA1 evolved to be increasingly sensitive to heat, activating at temperatures as low as 80 degrees Fahrenheit (18 degrees cooler than the normal human body temperature). This TRPA1 gene is described to be millions of years old, but the viper and other snake species that use infrared sensing are much younger in comparison.
I think that the analysis of the infrared sensing genes in the snake species as well as other animal species is a really great way to demonstrate evolutionary abilities of genetics. It's incredible the a gene that is also found in humans to be able to feel heat when tasting spicy things, can vary so differently as to code for infrared sensing organs in snakes. I think the New York Times article does the best job by stating "evolution of new abilities does not necessarily require new genes, but new variations of old genes".